Polyurethanes and polyisocyanurates are known generally in the art as being polyisocyanate-derived polymeric products. These products can be foamed or non-foamed, the former type receiving significant interest as an insulative and cushioning material in many and various industries during the past few years. The foamed polyurethanes are generally prepared by reacting the polyisocyanate with the polyol in the presence of a blowing agent (e.g., a normally gaseous fluorocarbon or carbon dioxide), the blowing agent expanding the reaction product during the reaction to produce a foamed or cellular structure. The polyurethane foams are characteristically and inherently non-heat-stable. Foamed polyisocyanurates are generally produced by reacting polyisocyanates in the presence of a trimerization catalyst and a blowing agent, the isocyanurate moiety imparting greater stability to the polymer. Where the polyisocyanate is a urethane prepolymer, or where it is trimerized in the presence of polyol, the resulting polymer contains urethane as well as isocyanurate linkages. The foamed products can be of high or low density, depending upon the amount of blowing agent used, and either rigid or flexible, depending upon the particular reactants used.
These foams can be generally referred to as poly (urethane-isocyanurates) or as urethane-modified polyisocyanurate foams. It is within the field of urethane-modified polyisocyanurate foams (sometimes referred to herein as polyisocyanurate foams) that the present invention resides.
Although semi-rigid and rigid polyisocyanurate foams (i.e., those having a high percentage of isocyanurate linkages) have generally better heat stability and structural strength than conventional polyurethane foams, the polyisocyanurate foams are characteristically friable and accordingly are not generally useful in energy absorbing panels. Similarly, such foams are not generally useful as structural members because of their friability and/or brittleness. Conventional urethane-modified polyisocyanurate foams tend to be less brittle and friable but also tend to exhibit less heat stability and also tend to be too low in strength to permit their use in structural members. Although these foams generally exhibit improved strength at higher densities, the attendant cost and weight considerations render use of such foams impractical.
Although there has recently been provided a urethane-modified polyisocyanurate foam with improved heat-stability and adhesion to oil-contaminated substrates, such foams do not exhibit the high levels of structural strength and energy absorption properties needed for certain applications. Also, such foams at higher densities do not exhibit the heat-stability required for certain applications.
There has now been discovered, however, certain poly(urethane-isocyanurate) foams which exhibit even further improved heat-resistance, compression and flexural strength and energy-absorption characteristics, which makes such foams especially suitable for use in energy absorbing structures and load bearing structures.